The Local Coordination Committee, a grassroots activists' organisation, said 17 people were killed in one raid alone, on a square in the city. Video footage showed fighters putting dismembered bodies in an ambulance.

Thousands of families, many of whom are already refugees from the neighbouring provinces of Aleppo and Deir al-Zor, have been fleeing Raqqa to surrounding countryside since it came under heavy aerial bombardment following an announcement by the opposition on Monday that it was captured, the sources said.

"There were about 25 air raids on Raqqa today. The civilian population is being driven out," said activist Abdallah Abu Gheith.

The poor, sandswept city, whose economy was devastated by a water crisis that hit grain and cotton production in the east before the revolt, is situated on the Euphrates River, 160 kms (100 miles) east of Syria's industrial and commercial hub of Aleppo.

Photographs taken by activists purportedly showed the education department building gutted by bombardment, and the body of a loyalist sniper they said was killed in a battle to take a military intelligence compound in the centre of the city.

Another activist working with refugees said most of the refugees have moved to the rural environs of Raqqa but lack of food and facilities there means they could soon head to Turkey, which already hosts many thousand Syrian refugees.

Opposition sources and residents said rebel fighters captured Raqqa on Monday and toppled a statue of President Bashar al-Assad's father, in what would be the first major city to be captured since the revolt erupted against four decades of Assad family rule in March 2011.